The invention relates to a method and a device for positioning a part that is movable by a drive back and forth between two end positions.
German Published Patent Application No. 195 27 456 describes drive systems for positioning a part, the part being moveable back and forth between two end positions by a drive, and upon reaching the end positions, a control signal being generated for the drive which stops the drive or reverses its driving direction. When reaching at least one of the end positions for the first time, the position of the drive is detected and stored, and when the part approaches this end position the next time, the drive is stopped before reaching the end position, or its driving direction is reversed. In this manner, the part to be positioned is already stopped in time, so that a mechanical stop is omitted with this limit stop. This reduces the mechanical stress of the entire system, particularly of the drive motor. Furthermore, after a selectable, definitively specified number of approach intervals toward the end position, the part is no longer stopped before reaching the end position, but rather the part to be positioned is driven toward the end position for the purpose of readjusting the entire drive system. In this context, a renormalization is carried out at regular intervals, and thus discernible by the user (driver).
According to the method of the present invention, a random number generated by a control unit predefines the number of approaches toward one or both of the end positions until a further readjustment of the drive system.
It is particularly advantageous that only random numbers are used which lie within stipulated minimal and maximal limiting values. The limiting values ensure that the system is readjusted or renormalized at useful time intervals. The intervals can preferably be determined by trial by the vehicle manufacturer, so that changes in the system such as friction changes caused by temperature, manifestations of material aging, accumulated inaccuracies in detecting position, and further deviations occurring during the operation of the drive system can be compensated for by renormalization.
Such a method is particularly suitable for drives of sliding sunroofs, tilt/slide sunroofs, power-window units, as well as for seat-adjustment systems or the like in a motor vehicle. In each case, there are one or two end positions which, according to the method of the present invention, are only run into for renormalizing the system.
Preferably one of these end positions is stipulated for renormalizing the system. This end position is run into during the first approach, as well as during each renormalization after the approach cycles predefined by the random number have expired. For example, in the case of a tilt/slide sunroof, the tilt position is suitable as the end position which can be run into, since usually an end position which can be run into does not exist in the slide position.
It is also conceivable to run into both end positions automatically in alternation for the purpose of readjusting the system.
It is further advantageous that the random number is generated by the control unit and is decremented in response to each approach of the part to be positioned to this end position.